This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2

See: meta.stackexchange.com/questions/21788/how-does-editing-work ("Multiple edits made by the same person may be combined into a single revision, if they occur within a short period of time." - currently, that window is 5 minutes - edits made within that window count as a single revision; edits within 5 minutes of posting count as the first revision)
–
Shog9♦Mar 26 '10 at 18:50